1. Field of the Invention
The present invention relates to an Mn—Zn ferrite, a transformer magnetic core and a transformer, and particularly relates to an Mn—Zn ferrite used as a magnetic core of a power supply transformer, etc. of a switching power supply, etc., having a small power loss (core loss) particularly in a wide temperature range, exhibiting a little deterioration of core loss characteristics also under a furthermore higher temperature (in a high temperature storage test), and having an excellent magnetic stability, a transformer magnetic core and a transformer.
2. Description of the Related Art
In recent years, there have been increasing demands on a variety of electronic devices to be more compact, thinner and more advanced. A more compact and thinner power supply transformer, etc. has been also demanded in a switching power supply, etc. To obtain a more compact and thinner transformer, a reduction of a core loss of a magnetic core becomes essential. Furthermore, when considering an operation environment of a power supply, etc., a highly reliable magnetic core having a small core loss in a wide temperature range, furthermore, exhibiting a little deterioration of core loss characteristics under a high temperature (in a high temperature storage test) to prevent thermal burn-up of an electronic circuit, and having excellent magnetic stability is demanded.
Under such demands, proposals have been made to reduce a core loss in a wide temperature range by dissolving a suitable amount of Co in an Mn—Zn ferrite (refer to the Patent Articles 1 to 13).
Patent Article 1 the Japanese Unexamined Patent Publication No. 6-290925
Patent Article 2 the Japanese Unexamined Patent Publication No. 6-310320
Patent Article 3 the Japanese Unexamined Patent Publication No. 8-191011
Patent Article 4 the Japanese Unexamined Patent Publication No. 9-2866
Patent Article 5 the Japanese Unexamined Patent Publication No. 9-134815
Patent Article 6 the Japanese Unexamined Patent Publication No. 13-80952
Patent Article 7 the Japanese Unexamined Patent Publication No. 13-220146
Patent Article 8 the Japanese Unexamined Patent Publication No. 2002-231520
Patent Article 9 the Japanese Examined Patent Publication No. 61-11892
Patent Article 10 the Japanese Examined Patent Publication No. 61-43291
Patent Article 11 the Japanese Examined Patent Publication No. 4-33755
Patent Article 12 the Japanese Examined Patent Publication No. 5-21859
Patent Article 13 the Japanese Examined Patent Publication No. 8-1844
Here, the reason why a core loss can be made small in a wide temperature range by dissolving Co will be explained. A magneto crystalline anisotropy constant K1 is a factor of dominating a core loss, temperature characteristics of a core loss change with a temperature change of K1, and the core loss becomes a minimum value at a temperature under which K1=0 stands. To reduce the core loss in a wide temperature range, K1 has to be made close to 0 in a wide temperature range. This constant K1 differs depending on a constituting element of a spinel compound as a main phase of a ferrite, but in the case of an Mn—Zn ferrite, it is considered that temperature dependency of K1 is made less by dissolving Co ions, and an absolute value of a magnetic loss temperature constant can be made small.
As described in the above publications, proposals have been made to reduce a core loss in a wide temperature range by dissolving a suitable amount of Co in an Mn—Zn ferrite.
However, there is no description on a means to enhance stability and reliability of core loss characteristics under a high temperature (in a high temperature storage test) further to prevent thermal burn-up of an electronic circuit in consideration on an operation environment of a power supply, etc.